1. Field of the Invention
The invention relates to liquid crystal composites, and in particular to a layered inorganic material utilized to improve liquid crystal physical and optical properties.
2. Description of the Related Art
In 1968, RCA disclosed first liquid crystal display (LCD) and initiated a new display era. Several LCD modes as thin-film transistor (TFT), super twisted nematic (STN), and the like were subsequently developed, such that LCD is applied in various fields. Under low driving frequency, the liquid crystal of TFT-LCD is often subject to ionic charge effect, with impact on display properties such as voltage holding ratio, threshold voltage, flicker, image sticking effect, and the like.
Upon application of voltage, the ion charge effect of the liquid crystal layer may originated from impurities or the liquid crystal layer itself. If the ion exchange charges are well distributed in the liquid crystal layer upon application of voltage, the ion charges accumulate in the interface of the liquid crystal layer and the alignment layer (the electricity of the liquid crystal layer opposite to that of the alignment layer). The different electric double layers (EBLs) are formed due to the different distribution areas of the positive/negative charges, thereby reducing or even cancelling the voltage applied to the liquid crystal layer. When voltage is cancelled, the electric field of the EBLs cannot dissipate, and the ion charges reverse to well distribution. Before the ion charges are distributed, the pressure sensed by liquid crystal layer is provided by the ion charges accumulated in the interface of the liquid crystal layer and the alignment layer, and the pressure will decay to zero with time. Because the equivalent voltage of the liquid crystal layer depends on the equivalent field of the EBLs, it is important to reduce ion charge effect of the liquid crystal device in this field.
In 1948 Gabor performed basic experiments in wavefront reconstruction (then called “holography”), with application extending to data reservoirs and related fields. Current research in wavefront reconstruction focuses on storage materials and read/write technology, having evolved from static mode to real time, dynamic, volume, and integral modes. Various storage mechanisms have been developed in holography multiplexing, such as angular multiplexing, wavelength multiplexing, shifting multiplexing, orthogonal phase multiplexing, and random multiplexing. Related applications are widely used in 3D image reconstruction, image collection searches, space and time filters, and holographic optical elements.
Although photorefractive effect of inorganic crystals has a high response rate, no photovoltaic effect, and high two wave-mixing photo energy gain; it is difficult to apply the inorganic crystals in everyday use because the inorganic crystal growth is difficult and expensive.
In 1990, photorefractive effect of organic materials was observed, generating research into application of organic materials in holography optical storage. Preferred organic materials may be polymer dispersed liquid crystals (PDLC), and more preferably photo-sensitive polymers. Due to advantages such as greater dynamic range of index of refraction, simplified process, composition variation, and less costly row materials, the photo-sensitive polymers have become popular holography optical materials. The related devices are important for improving optical grating diffractive efficiency.
In 1998, Kawasumi et al dispersed modified clays in a bi-stable liquid crystal. Upon application of voltage to the bi-stable liquid crystal, the viscosity of the modified clay stabilizes the liquid crystal by delaying the relaxation time thereof. Note that the bi-stable liquid crystal and organic modified clay is necessary for Kawasumi et al. The invention further adopts natural clay and other layered inorganic materials.
In Japanese Pat. No. JP2003268373, the 0.05-10 wt % clay minerals and organic solvents are dispersed in a cholesterol liquid crystal to serve as a record display media. The liquid crystal composite of the invention excludes organic solvents, and further utilizing nematic and smectic liquid crystals.
In U.S. Pat. No. 6,928,028, the charged particles such as metal oxides are dispersed in a liquid crystal formed between two glass substrates, and the accumulation of the charged particles is controlled by pulse voltage and counter voltage for manufacturing a bi-stable LCD device. Note that U.S. Pat. No. 6,928,028 only discloses metal oxides other than any clay.
In 2004, Vaia et al dispersed modified clays in epoxy resins. According to Clausius-Mossotti principle, the applied voltage polarizes layered clays, with resulting orderly arrangement. After curing, the physical properties of the epoxy resins/clays are direction dependent, thereby proving the ordered arrangement of clays in the epoxy resins. Vaia et al utilizes epoxy resin, and the invention utilizes liquid crystals, respectively.
In U.S. Pat. Application No. 20050046782, 1 nm-50 nm inorganic oxides are coated on the glass substrates of a ferromagnetic or anti-ferromagnetic liquid crystal cell. The inorganic oxides can adsorb the free ions of the liquid crystal to reduce threshold voltage and retain voltage. U.S. Pat. Application No. 20050046782 utilizes inorganic oxides, and the invention utilizes other inorganic materials.
In U.S. Pat. Application No. 20050062927, C60 (of about 5 wt %) is dispersed in liquid crystal, thereby enhancing the light transmittance, response speed, contrast ratio, and view angle. Note that the C60 is an expensive material.
In 2005, Higgins et al disclosed a new method for controlling PDLC micro-drops, utilizing an optical microscope to determine the properties and manners of the micro-drops. The response time of the drops can be determined by the micro-drops rotation induced by electric field. Note that there is no material dispersed in the PDLC of Higgins et al.
Accordingly, a layered inorganic material dispersed in liquid crystal for improved optical grating diffractive efficiency is called for.